The present invention relates to an electronic camera, particularly to an electronic camera having a solid-state image pickup device.
Various electronic cameras have heretofore been proposed which comprise image pickup means including a solid-state image pickup device and in which the duration of charge storage in the device is controlled to thereby control the amount of charges to be stored, i.e., the amount of exposure. For example, Unexamined Japanese Patent Publication No. 61-26376 and U.S. Pat. No. 4,758,883 disclose electronic still video cameras which comprise an aperture diaphragm stopping-down mechanism and a shutter mechanism for controlling the amount of light incident on the image pickup means and controlling the duration of charge storage in the solid-state image pickup device.
Further with solid-state image pickup devices realized which are controllable at a high speed in the charge storage duration, U.S. Pat. No. 4,742,395 discloses a still video camera which includes no aperture diaphragm stopping-down mechanism or shutter mechanism and in which only the charge storage duration of such a pickup device is controlled to give a controlled amount of exposure. More specifically, the solid-state image pickup devices realized are generally about ISO 50 (Sv=4) in exposure sensitivity in terms of film sensitivity and about 1/4000 second (shutter speed Tv=12) in the highest controllable value of charge storage time. When an objective lens with an aperture size F=2.8 (Av=3) is used in combination with such an image pickup device, the maximum value of the luminance Bv of objects which can be photographed is Bv=Tv+Av-Sv=12+3-4=11, so that the amount of exposure for taking usual photographs is controllable by controlling only the charge storage time of the device without using the aperture diaphragm stopping-down mechanism, shutter mechanism or like exposure control means.
When the exposure control means is dispensed with, the camera can be simplified and less costly, whereas there arises a need to alternatively provide an incident light blocking member for preventing the light through the objective lens from impinging on the image pickup means. In the absence of the exposure control means which also serves to block the incident light, the incident light always impinges on the image pickup means, causing discoloration of the optical filter within the pickup means or reducing the exposure sensitivity of the image pickup device, hence the necessity of the light blocking member.
Furthermore, with electronic cameras incorporating a solid-state image pickup device, it is known to control the flash firing (emission stating) time.
For example, Unexamined Japanese Patent Publication No. 58-147719 discloses a camera which incorporates image pickup means of the charge storage type and in which a command is given for flashlight photography or a flashlight photography mode is automatically set upon the duration of charge storage of the image pickup means exceeding a predetermined period of time so as to assure an image pickup signal of specified level.
Further Unexamined Japanese Patent Publication No. 58-147722 discloses a system wherein a flash unit functions automatically upon the duration of charge storage of image pickup means reaching a predetermined time interval and discontinues the emission of light when a proper amount of exposure is obtained to complete charge storage.
Unexamined Japanese Patent Publication No. 58-147723 discloses a system adapted to control the duration of charge storage of image pickup means to a short time interval for flashlight photography to diminish the increase in dark current due to a long period of charge storage and thereby assure improved S/N.
Since the charge storage duration is inherently limited if long, insufficient exposure will result if the object is dark. The techniques disclosed in the above publications are concerned with the control of charge storage duration or the emission of light by the flash unit when the insufficient exposure is to be corrected with the auxiliary light of the flash unit.
Unexamined Japanese Patent Publication No. 58-104573 discloses a system adapted to avoid useless flashing by synchronizing the start of charge storage of a solid-state image pickup means with the firing of a flash unit and also synchronizing the termination of light emission by the flash unit with the start of transfer of the stored charge.
The flashlight control systems disclosed in the foregoing publications for use in electronic cameras with the solid-state image pickup device are advantageous in that the signal charge storage duration is controllable (at a high speed) as desired, whereas there arises a need to adjust the flashlight with the available light in flash photogtaphy when it is attempted to always ensure proper exposure for objects which vary widely in luminance.
With the systems, such as those stated above, which are adapted to control the flashlight after starting a photographic operation, the flashlight is used to photograph the main object, such as a person, rather than a view in its entirety, with the result that the entire photograph obtained involves a marked difference in brightness between the background and the person, failing to reproduce the view beautifully. For example, when a person is photographed against a night view using flashlight, the person is photographed with an exceedingly higher brightness than the background in sharp contrast therewith, and the photographed scene appears different from the actual one. Furthermore, the amount of flashlight needed differs with the photographing conditions, e.g., front lighting or back lighting, or with the size of the object relative to the entire image area. Thus, the conventional control systems encounter difficulties in photographing objects beautifully despite varying conditions while reproducing the actual scene properly in conformity with the particular condition involved.